Effect of hot and humid conditions on cortisol levels in lactating dairy cows

Abstract EN

Fourteen lactating, non-pregnant Holstein co^s were heat synchronized for estrus and assigned randomly to pens in a freestall barn with (Fan) or without (Control) a fan to observe the effect of forced ventilation on cortisol concentrations.

After a 21-day adjustment period, jugular cannulae wei'e inserted for blood sampling before PGF2a injection.

All animals were in their luteal phase at the time of injection as determined by previous observations for estrus and palpation.

After PGF2a, blood samples were collected at 6-h intervals from 0 to 36h, 4-h intervals from 36 to 88h and 3 times weekly for three weeks thereafter.

Blood samples were assayed for cortisol.

Daily l'ectal temperatures and ambient data were recorded.

Average daily rectal temperatures were lower (PC0.05) in the Fan (39.1"C) than in the Control (39.5"C).

Cortisol did not show a diurnal pattern and the values did not differ (P >0.05) between treatment groups.